Death-defying comet wags its tail during solar embrace

The sun’s atmosphere – the corona – is too hot for spacecraft to explore. Luckily, there’s a family of comets that isn’t afraid to plunge in, allowing us to probe this mysterious region.

In 2011, one of these sun-grazers, named Lovejoy, became the first comet seen to dive through the sun’s corona and emerge intact, – at least for a while (see video). In visible light, the corona is about a millionth as bright as the sun’s surface, so images of it are usually captured in extreme ultraviolet. In the video above, Lovejoy’s ice vaporises as it passes through the corona, forming a tail of plasma that shines brightly in extreme UV. Interestingly, the tail moves erratically compared with the comet’s trajectory.

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According to a team led by Cooper Downs of Predictive Science in San Diego, California, the wiggling is caused by the sun’s magnetic field. The researchers are matching the tail’s motion with computer models of the corona’s magnetic field, as shown in the video, to explore magnetic activity on the sun.

“We care about the magnetic field in the corona, because the structure and dynamics of this field dictates the nature of the solar wind and solar eruptions,” says Downs.

The team has applied data obtained from Lovejoy to two competing models of the magnetic field, but it’s too early for definitive results.

Astronomers are expecting a cluster of sun-grazers to come charging at the sun over the next decade, giving us plenty of opportunities to gather more details. In fact, a large comet called C/2012 S1 (ISON) is expected to come within 1.2 million kilometres of the solar surface this November. “If its tail lights up as brightly as Lovejoy’s, the solar encounter could offer a nice probe of the birth region of the solar wind”, says Downs.